Paint application seems to be one of those more difficult areas of modeling
to master. It's not an exact science, and the number of variables involved and
how they affect one another along with finish quality, can befuddle even an
experienced painter. And while a lot of great tips, advice, and techniques
show up almost everywhere, troubleshooting paint problems sight unseen, is
still pretty tough.

So, to add to the troubleshooting information arsenal, I shoveled the dust
off of my old reference books and put together a list of paint problems and
their causes. Notice I didn't say a complete list. This list is
by no means complete, as plenty of other problems exist, but I tried to pare
it down to those that are more likely to be encountered in the little booth.

It's all in alphabetical order and broken down into four areas: Condition,
Cause, Prevention, and Remedy. The numbered items in Cause and Prevention are
relative to one another, for example, Cause number 1 for a given problem can
be avoided by Prevention number 1 for that same problem.

I hope you find it useful.

Klaus

BLEEDING

Condition: A change in color of the paint that results from the
pigment, or other colored material in the surface beneath the coating, moving
upward into the applied film and becoming visible.

Cause: 1. Contamination, in the form of soluble dyes or pigments
(especially red), on the older finish before it was repainted.

2. Wrong thinner or reducer - too slow.

Prevention: 1. Thoroughly clean the areas to be painted before and
after sanding, especially when applying lighter colors over darker colors.
Avoid using lighter colors over older shades of red without applying a sealer
first.

2. Select the thinner or reducer most suitable for existing shop
conditions.

Remedy: Apply a sealer before reapplying the color coat.

BLISTERING

Condition: Bubbles or pimples that appear in the topcoat film,
sometimes months after application.

Cause: 1. Improper surface cleaning or preparation. Dirt left on the
surface can act as a sponge and hold moisture. When temperature or atmospheric
pressure increases, the moisture expands and builds up pressure, resulting in
blisters.

2. Wrong thinner or reducer. Use of a fast-dry thinner or reducer,
especially when the material is sprayed too dry or at an excessive pressure,
can result in air or moisture being trapped in the film.

3. Excessive film thickness. Insufficient drying time between coats or too
heavy an application of the undercoats can trap solvents that later escape and
blister the color coat.

4. Contamination of compressed air lines with oil, water or dirt.

Prevention: 1. Thoroughly clean the areas to be painted before and
after sanding. Ensure all surfaces are dry before applying coatings. Avoid
touching the cleaned area with your bare hands to prevent skin oil from
contaminating the surface.

2. Select the thinner or reducer most suitable for existing shop
conditions.

3. Allow proper drying time for undercoats and topcoats. Be sure to let
each coat flash before applying the next coat.

4. Drain and clean air pressure regulator and drain air compressor tank
daily.

Remedy: In mild cases, the blisters can be sanded out, and refinished.
If damage is severe, the paint must be removed down to the undercoat or
substrate, depending on the depth of the blisters, and then refinished.

BLUSHING

Condition: A milky white haze that appears on the paint film.

Cause: 1. In hot humid weather, moisture droplets become trapped in the
wet paint film. Air currents from the spray gun, spray booth ventilation, and
evaporation of the thinner tend to make the surface being sprayed lower in
temperature than the surrounding atmosphere. This causes moisture in the air
to condense on the wet paint film.

2. Excessive air pressure.

3. Wrong thinner - too fast.

4. Low temperatures of the part, paint, and spray booth air, increase the
chance of dropping below the dew point.

2. Thoroughly clean the areas to be painted before and after sanding.
Ensure the surface is completely dry before applying undercoats and topcoats.

Remedy: Remove topcoat down to the primer and apply new topcoat.

CHECKING (MICRO-CHECKING)

Condition: Appears as severe dulling of the film, but when examined
with a magnifying glass, it contains many small cracks that do not touch.
Micro-checking is an indication that cracking or crazing may develop.

Remedy: Remove the topcoat down to primer and apply new topcoat

CRACKING

Condition: A series of deep cracks resembling cracks in a dry pond,
often going all the way through the topcoat and undercoat

Cause: 1. Excessive film thickness that magnifies normal stresses and
strains in the paint film

2. Poorly mixed materials.

3. Insufficient flash time.

4. Incorrect use of additive.

Prevention: 1. Allow sufficient flash and dry time between coats. Do
not dry the coatings by gun fanning.

Remedy: Sand the affected areas to a depth below the damage, and
refinish.

CRAZING

Condition: Fine splits, small cracks, or crowsfeet, that completely
checker an area in an irregular manner.

Cause: 1. Shop too cold, literally causing the original material to
shatter under the softening action of the solvents being applied.

Prevention: 1. Select the correct thinner or reducer for existing shop
conditions. Schedule painting to avoid temperature and humidity extremes in
the shop; bring the part to room temperature before painting.

Remedy: 1. Apply wet coats of the topcoat with the wettest thinner shop
conditions will allow, to melt the crazing and flow the pattern together.

2. Apply a fast-flashing topcoat to bridge over the cracks in the crazing
area.

FEATHEREDGE SPLITTING

Condition: Appears as stretch marks or cracking along the edge of a
refinished area (featheredge); occurs during or shortly after a new topcoat
application

Cause: 1. Piling on the undercoat causes solvent to become trapped in
undercoat layers that have not had time to set-up.

2. Poor mixing of materials, causes the paint to act like a sponge. As the
solvent flashes the finish shrinks and pulls away from the refinished area.

3. Wrong thinner.

4. Improper surface cleaning or preparation. When not properly cleaned,
primer-surfacer coats draw away from the edge because of poor adhesion.

5. Improper drying. Fanning with a spray gun after the primer-surfacer is
applied results in drying the surface before solvent or air from the lower
layers is released.

6. Excessive use and buildup of putty during the refinishing process.

Prevention: 1. Apply primer-surfacer in thin to medium coats with
enough time between coats to allow solvents and air to escape.

2. Mix all materials thoroughly.

3. Select only thinners that are suitable for existing shop conditions.

4. Thoroughly clean areas to be painted before and after sanding.

5. Same as #1.

6. Lacquer putty should be used in minimum amounts, applied in thin layers.
Putty applied too heavily will eventually shrink and cause featheredge
splitting.

Remedy: Remove finish from the affected areas and refinish.

FISH EYES

Condition: Small crater-like openings in the finish

Causes: 1. Improper surface cleaning or preparation, usually involving
deposits of silicone or wax on the surface of the old topcoat.

2. Effects of an old finish with embedded silicone that is not removable by
solvent wiping.

3. Oil contamination of air lines.

Prevention: 1. Remove all traces of silicone or wax by thoroughly
cleaning with a product designed for this purpose.

2. Add fish eye eliminator to the topcoat.

3. Drain and clean the air pressure regulator daily.

Remedy: After the affected coat has set up, apply a double coat of
color containing the recommended amount of fish eye eliminator. In severe
cases, the affected area should be sanded down and refinished.

LIFTING

Condition: Distortion or shriveling of the surface while the topcoat is
being applied or drying.

Cause: 1. Incompatible materials. Solvents in the new topcoat attack
the old surface, e.g., lacquer over enamel.

2. Insufficient flash time or drying between coats.

3. Improper surface cleaning or preparation.

4. Wrong thinner or reducer.

Prevention: 1. Use only materials that are compatible with the old
surface, and designed for use with one another.

2. Don't pile on topcoats. Allow sufficient flash and drying time. Topcoats
should be applied when the previous coat is still soluble or after it has
completely dried and is impervious to the topcoat solvents.

3. Thoroughly clean the areas to be painted before and after sanding.
Ensure the surface is completely dry before applying undercoats and topcoats.

4. Use a thinner or reducer that is recommended for the topcoat being
applied and is suitable for existing shop conditions.

Remedy: Remove the finish from the affected area and refinish.

MOTTLING

Condition: A stripped or spotty appearance in metallic paints caused by
the flakes floating together in the paint film

Condition: Dimpled surface, like the skin of an orange, resulting from
paint droplets drying too much to level out and flow smoothly together (poor
coalescence)

Cause: 1. Improper gun adjustment and techniques.

2. Extreme shop temperature causing the droplets to lose more solvent and
dry out before they can flow and level properly.

3. Improper drying by gun fanning causing the paint droplets to dry out
before they have a chance to flow together.

4. Improper flash or drying time causing subsequent coats to lose solvents
to the dry coat.

5. Wrong thinner or reducer, or too little thinner or reducer.

6. Poor mixing of materials.

Prevention: 1. Use proper gun adjustments, techniques, and air
pressure.

2. Schedule painting to avoid temperature and humidity extremes. Select
thinner or reducer that is suitable for existing conditions. Use a slower
evaporating thinner or reducer to overcome this.

3. Allow sufficient flash time. Do not dry by fanning.

4. Allow proper dry time for undercoats and topcoats.

5. Use the correct thinner and reducer in correct amounts for existing shop
conditions.

6. Mix all pigmented coatings thoroughly.

Remedy: In mild cases, a mild polishing compound for enamel or rubbing
compound for lacquer may help. In severe cases, sand and refinish with a
slower evaporating thinner or reducer at the correct air pressure.

PEELING

Condition: Loss of adhesion between the paint and substrate

Cause: 1. Improper cleaning or preparation. Dust or other surface
contaminants preventing the paint film from coming into proper contact with
the substrate.

2. Poor mixing of materials.

3. Use of incorrect primer/sealer, or no primer/sealer.

Prevention: 1. Thoroughly clean areas to be painted.

2. Mix all pigmented coatings thoroughly.

3. Primer/sealers are generally recommended to improve adhesion of
topcoats.

Remedy: Remove finish from an area slightly larger than the affected
area and refinish.

PINHOLING

Condition: Tiny holes in the finish, putty or body filler, usually the
result of trapped solvents, air or moisture

3. Avoid piling on undercoats or topcoats. Allow sufficient flash and dry
time. Do not dry by fanning.

Remedy: In mild cases, the damage can be sanded out, and refinished. If
damage is severe, the paint must be removed down to the undercoat or
substrate, depending on the depth of the holes, and then refinished.

WET SPOTS

Condition: Spots of various sizes that are discolored, slow drying, or
both.

Cause: 1. Improper cleaning and preparation.

2. Improper drying or excessive undercoat film build.

3. Wet sanding with contaminated solvent.

Prevention: 1. Thoroughly clean all areas to be painted.

2. Allow sufficient flash and dry times for undercoats.

3. Use water when wet sanding.

Remedy: Solvent wash or sand affected areas thoroughly and refinish.

WRINKLING

Condition: Surface distortions or shriveling that occurs while the
enamel topcoat is being applied or drying.